Air strikes have hit Douma in Syria's rebel-held Eastern Ghouta just after 13 trucks of food aid crossed into the enclave, heading for the town, according to opposition activists and a monitor.

The development came on Friday after an overnight pause in fighting encouraged the International Committee of the Red Cross (ICRC) to send the convoy in, that had previously been delayed due to violence.

The UK-based Syrian Observatory for Human Rights (SOHR) had previously said that the besieged enclave had witnessed no air strikes for the first time in the last 10 days.

However, shortly after the aid convoy crossed into the enclave on Friday, the SOHR said, the air strikes resumed.

The UN estimates that 400,000 people live in the rebel-held areas of Eastern Ghouta.

The attack on Douma as the aid convoy entered the area is part of a larger trend. On Friday, the World Health Organization verified 67 attacks on health facilities in the first two months of 2018.

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In less than two weeks, the Syrian army has retaken nearly all the farmland in Eastern Ghouta, under cover of near-ceaseless shelling and air strikes, leaving only handful towns - about half the enclave - still under rebel control.

The SOHR on Friday said at least 931 civilians have been killed since February 18.

According to Doctors Without Borders (MSF), more than 1,000 people have been killed.

'Safe routes'

UN aid agencies have pleaded with the Syrian government and its ally, Russia, to halt the air campaign and allow access.

Syria and Russia have both said the assault is needed to stop rebel shelling of Damascus.

The government and Russia's military have opened what they say are safe routes out of the enclave, but nobody has left yet.

The two allies accuse the Syrian rebels of shooting at civilians to prevent them from fleeing the fighting into government areas.

The rebels deny the accusation and say the area's inhabitants have not crossed into government territory because they fear persecution.